Dopant-Chelating Polymeric Hole Transporting Material for Efficient and Humidity-Stable Quantum Dot Photovoltaics

Abstract

Although conjugated polymers (CPs) have been extensively investigated as hole transport layers (HTLs) for optoelectronic devices, including colloidal quantum dot (CQD) photovoltaics, their stability is often limited by dopant-induced diffusion into the underlying photoactive regions. To overcome this, an ionic-electronic CP, PBTBDF-TEG, comprising benzodifuran and tetraethylene glycol (TEG)-substituted furan units is designed. PBTBDF-TEG effectively confines lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopants via lithium chelation by the TEG side chains, thereby suppressing dopant migration. This coordination also reduces the (010) π–π stacking distance, promoting hole transport by alleviating steric hindrance. Consequently, CQD solar cells incorporating LiTFSI-doped PBTBDF-TEG exhibited a power conversion efficiency (PCE) of 13.7%, exceeding the 11.8% achieved with the undoped counterpart. Furthermore, lithium chelation immobilizes water molecules, mitigating moisture ingress. As a result, the doped device retained over 90% of its initial PCE after 24 h under high humidity (85%–95% RH), whereas the undoped device exhibited substantial degradation.